Method of drying wet materials



Patented Oct. 14, 1930 UNITED STATES PATENT OFFICE Rama EMANUEL KRISIENSSON, or Lxnmeo, swnmm, ASSIGNOB 'ro Ax'rmnomcn'r 131315365 noevaouuuruur, or s'rocxnomu, SWEDEN METHOD OF DRYING WET MATERIALS Ho Drawing. Application filed October 18, 1929, Serial No. 400,742, and in Sweden November 28, 1988.

It is known to dry wet materials in vacuum in such manner that the material is heated by means of direct steam in a drying chamber whereupon the chamber is evacuated by 5 means of a pump, the steam removed being to the greater part condensed in a condenser provided between the drying chamber and the pump. Said method is generally carried out in the following manner. The drying chamber is charged with the wet goods to be dried and then closed with the exception of an outlet valve which is left open. Then steam of a pressure of for instance 2 to 4 atmos- 5 pheres is supplied to the chamber, the air contained in the chamber being expelled through the open outlet valve while the goods and the walls of the drying chamber being heated. The heating is, if desired, amplified 9 by indirect heating, for instance by means of steam heated coils provided in the drying chamber. When the goods to be dried has attained the desired temperature, which for wood amounts to about 70 to 95 C., the out- 3 let valve is closed and the supply of heating steam is cutofi'. Then the Vacuum pump is started, so that steam and the remainder of air is removed from the drying chamber, the

steam being condensed in the condenser pro- 9 vided between the drying chamber and the pump. The pressure in the drying chamber sinks rapidly and when it has reached a Value corresponding to the pressure of saturated steam at the temperature of the goods to be dried, the water content ofthe goods begins to evaporate. By continuing the evacnation and the condensation, the equilibrium: between the temperature of the wet goods and the pressure of the saturated steam in' the drying chamber is maintained. The heat stored in the walls of the drying chamber and in the wet goods causes a continued generationof steam which, if desired, isincreased by an indirect supply of heat. When the condensation in the condenser has decreased to a slight value which occurs when the temperature of the goods has decreased to about to 40 C. if the cooling water available for thecondenser has a temperature of about 15 C. the evacuation is interrupted. Air is then supplied to the drying chamber so as to restore the atmospheric pressure and the remaining moisture in the interior of the goods is given an opportunity to difiuse towards the surface. Then a renewed heating by direct steam followed by evacuation and restoring of the atmospheric pressure takes place which processes are repeated until the v expelling the air present in said chamber and the goods and then alternately evacuating the drying chamber and supplying steam'to it in absence of atmospheric air while maintaining a pressure below the atmospheric pressure until the desired dryness of the goods has been attained.

As an example of carrying out the invention I will herebelow describe its application to the drying of wood. The wood to be treated is charged in a drying chamber, having preferably the form of a cylinder with a loose cover at one end. After the closing of the chamber steam of a pressure of 2 to 4 atmospheres is supplied, the supply of steam being controlled in such manner that the temperature of the wood is slowly raised to about 60 C. although it may at times be carried as high as (3., depending upon the character of wood being treated. The maximum temperature varies with the sort of the wood and should for resinous wood heating is preferably carried out at atmospheric pressure, the air contained in the drying chamber being expelled through an outlet valve by the steam supplied. When the charge has attained the permissible maximum temperature, the outlet valve is closed and the supply of steam is cut off. The drying chamber is then evacuated by means of a pump, the steam sucked ofi' from the drying chamber being to the greater part condensed in a condenser provided in the conduit between the drying chamber and the pump. When the condensing in the condenser has decreased to a low value which is the case when the temperature of the wood has decreased to about 20 to 40 C. if the temperature of the cooling water available for use in the condenser is about 15 C., the evacuation is interrupted. A renewed heat-- ing of the wood is now immediately efiected by supplying steam to the drying chamber while any supply of air to the drying chamber being avoided and the supply of steam being so controlled that a rather high vacuum is maintained in the chamber. By said supply of steam the temperature of the goods treated and of the walls of the drying chamher is again increased to the permissiblemaximum value. The pressure in the drying cylinder should at least during a par-t of the heating period not exceed 200 m. 1n. Hg and throughout the heating period is preferably maintained below atmospheric. During the heating period the steam supplied delivers partof its heat to the Wood. The condensate formed collects partly as drops or bodies of water on the wood and the Walls of the drying chamber but a considerable part thereof remains suspended as a mist in the cylinder and will be removed in said state in the subsequent evacuation without requiring any supply of heat for its evaporation. The process is repeated with alternate supply of steam while maintaining a desired vacuum and evacuation to a low pressure until the desired degree of dryness has been attained.

The process can be modified in such manner that a moderate supply of steam is maintained also during the evacuation periods, if desired in connection with indirect heating, the temperature and pressure in the cylinder being thus maintained approximately constant and at desired values by controlling the temperature and superheating of the steam supplied.

Besides the advantages of a shortened time of treatment and a reduced maximum temperature in comparison with known steam heating methods, my invention has also the advantage that the heating steam may be supplied at a higher pressure than hitherto and be-superheated,.it desired, in as much as the heating is interrupted each time at such an early stage that the material such as for instance wood, corn, fish, flesh and other albumin substances, bricks, pottery etc.

l/Vhat I claim is:

1. Method of drying wet materials, which comprises first heating the material in a drying chamber by means of direct steam substantially at atmospheric pressure while removing the atmospheric air from said chamber, and then alternately evacuating the drying chamber to a low pressure and supplying steam to reheat the material treated substantially in absence of atmospheric air until the desired degree of dryness has been attained, the reheating taking place at a pressure below the atmospheric pressure.

2. Method of drying wet materials, which comprises first heating the material in a drying chamber by means of direct steam substantially at atmospheric pressure while removing the atmospheric air from said chamber, and then alternately evacuating the drying chamber to a low pressure and supplying steam to reheat the material substantially in absence of atmospheric air until the desired degree of dryness has been attained, the reheating being started when the temperature of the material treated has fallen to about 35to 40 C. and being interrupted when the temperature of the material has been raised to at most 60 C. i 3. Method of drying wet materials, which comprises first heating the material in a drying chamber by means of superheated direct steam at atmospheric pressure while removing the atmospheric air from the drying chamber, and then alternately evacuating the drying chamber to a pressure below 200 m. m. Hg and supplying superheated steam to reheat the material treated substantially in absence of atmospheric air, until the desired dryness has been attained, the reheating being each time interrupted before the pressure in the heating chamber has reached the atmospheric pressure.

4. The method of drying wet material which comprises introducing the same into a drying chamber, withdrawing atmospheric air from said chamber, heating the material by means of direct steam while maintaining the pressure below atmospheric, and then alternately evacuating the chamber to a low sub-atmospheric pressure and supplying steam to reheat the material while maintaining at substantially all times pressure below atmospheric until the desired degree of drynws has been attained,

- nately evacuating the chamber to a low pressure and supplying steam to reheat the material treated, while excluding atmospheric air and maintaining at substantially all times pressure below atmospheric until the desired degree of drynesshas-been attained.

6. The method of drying wood which comprises introducing the wood into a drying chamber, removing atmospheric air from the chamber, heating the wood in the chamber by means of direct steam and alternately evacuating the chamber to a sub-atmospheric pressure and supplying steam to reheat the material in the absence of atmospheric air 11. The method of drying material which comprises introducing t e same into a drying chamber, withdrawing atmospheric air from said chamber, heating the material by means of direct steam and then alternately evacuating the chamber and introducing direct steam, the ressure in the evacuating steps and throug out the greater portion of the individual heating steps being maintained below atmospheric.

12. The method of dr ing material which comprises introducing the same into a drying chamber, withdrawing atmospheric air from said chamber, heating the material by means of direct steam and then alternately evacuating the chamber and introducing direct steam, the ressure in the evacuating steps and throug out the greater portion of the individual heating steps being mainwhile excluding atmospheric air and maintained below atmospheric, and air being extaining the pressure in the heating and evaceluded throughout.

uation below atmospheric, the reheating being started when the temperature of the ma- .terial has fallen not lower than 20 C. and

' comprises introducing the same into a drying chamber,heating the material by means of direct steam,-evacuating the drying chamber and then alternately introducing steam and evacuating While maintaining substantially Miv throughout the treatment less than atmospheric pressure. g

8. The method of drying material which comprises introducing the same into a drying chamber, heating the material by means of direct steam, evacuating the drying chamberand then alternately introducing steam and evacuating while excluding atmospheric air and maintaining substantially throughout thetreatment less than atmospheric pressure.

9. The method of drying material which comprises introducing the same into a drying chamber, withdrawing atmospheric air and heating the material by means of direct steam, evacuating the chamber and then alternately introducing steam and evacuating, the reheating being started when the temperature of the material has fallen to not less than 20 C. and being interrupted before the pressure substantially exceeds atmosheric.

10. The method of dr ing material which comprises introducing t e same into a drying chamber, withdrawing atmospheric air and heating the material by means of direct steam, evacuating the drying chamber and then alternately introducing steam and evacuating, the reheating being each time interrupted before the ressure in the heating chamber substantia ly exceeds atmospheric pressure. I

' 13. The method of drying material which comprises introducing the same into a drying chamber, withdrawing atmospheric air from said chamber, heating the material by means of direct steam and'then alt'ernatel evacuating the chamber and introducing di-' rect steam substantially in the absence of atmospheric air, the pressure in the evacuating steps and throughout the greater portion of the individual heating steps being maintained below atmospheric.

14. The method of drying material which comprises introducing the same into a drying chamber, withdrawing atmospheric air from said chamber, heating the material by means of direct steam and then alternately evacuating the chamber and introducing direct steam substantially in the absence of atmospheric air, the pressure in the evacuating steps and throughout the greater portion of the individual heating steps being maintained below atmospheric, and air being excluded throu hout.

15. he method of drying wood which comprises introducing the same into a drying chamber, withdrawing atmospheric air from said chamber, heating the wood by means of direct steam and then alternately evacuating the chamber and introducing direct steam, the pressure in the evacuating steps and throughout the greater portion of the individual heating steps being maintained below atmospheric, each time resuming the heating when the temperature falls to not less than 20 C., and interruptin the same below a temperature which won d cause effusions of rosin or similar wood content.

16. The process of drying substances which consists in altering the temperature thereof by subjecting the same to direct steam, maintaining sub-atmospheric pressure substantially throu bout the steam treatment, and then drying y evacuation.

17. The process of drying substances which consists in altering the temperature thereof by subjecting the same to direct steam, maintaining sub-atmospheric pressure substantially through the steam treatment, and also substantially excluding atmospheric air and then dr ing by evacuation.

18. he process of drying substances which consists in subjecting the same first to steam under atmospheric pressure and then alternately (a) drying by evacuation and (b) supplying additional heat by subjecting the substances to direct steam while maintaining sub-atmospheric pressure substantially through the steam treatment.

19. The process of dr ing substances which consists in subjecting t e same first to steam under atmospheric pressure and then alter,-

nately (a) drying by evacuation and (b) supplying additional heat by subjecting the substances to direct steam while maintaining sub atmospheric pressure substantially throughout the steam treatment and also substantially excluding atmospheric air.

In testimony whereof I have signed my name.

' ROBERT EMANUEL KRISTENSSON. 

